ASTRAL HEAT. 407 



observations agree upon this point, the .very elaborate ex- 

 periments of Lichtenfels and Frohlich show that these 

 periods are well-marked, even when no food is taken. 1 

 Barensprung and Ladame further show that the fall in tem- 

 perature during the night takes place sleeping or waking ; 

 and that when sleep is taken during the day it does not 

 disturb the period of the maximum, which occurs at about 

 four p. M.* 



According to these experiments, at eleven in the morn- 

 ing, the animal heat is at one of its periods of maximum ; it 

 gradually diminishes for two or three hours and is raised 

 again to the maximum at about four in the afternoon, when 

 it again undergoes diminution until the next morning. The 

 variations amount to from about 1 to 2*16. The minimum 

 is always during the night. 



The relations of the animal temperature to digestion are 

 still somewhat indefinite. It is well known that activity 

 of the digestive organs increases the consumption of oxygen, 

 and, to a corresponding degree, the exhalation of carbonic 

 acid ; but we have to assume that the production of heat is 

 in direct ratio to the respiratory action in order to establish 

 any relation between calorification and the digestion of 

 ordinary food. It is easy to calculate that a given amount 

 of oxygen will produce a definite quantity of carbonic acid, 

 and will, by its union with carbon and hydrogen, generate a 

 certain number of " units of caloric ; " but the mechanism of 

 the production of animal heat is too complex and not well 

 enough understood to admit of such positive reasoning. 

 There is, indeed, no experimental evidence of any marked 

 and constant change in the general temperature of the body 

 during the ordinary process of digestion ; but it is none 

 the less true that the quantity and quality of food bear 



1 LICHTEXFELS UNO FROHLICH, Beobacldungen uber die Gesetze des Ganges der 

 Pulzfrequenz und Korperwdrme in den normalen Zustanden. Denkschriften der 

 kaiserlichen Akad. der Wissenschaften, maihematiscli-naturwissenschaftliche Classe, 

 Wien, 1852, Bd. iii., Zweite Abth., S. 113, et seq. 



2 LOXGET, Traite de physiologic, Paris, 1869, tome ii., pp. 499, 534. 



